1. Field of the Invention
The present invention relates generally to electronic document distribution and more particularly to a reusable, high resolution, display providing visual characteristics comparable to hard copy print.
2. Description of Related Art
There is growing interest in electronic document distribution in place of hard copy. The advent of the Internet facilitates distribution that provides virtually instantaneous access to document information while avoiding the high cost of printing, binding, warehousing, distribution, and retail mark-up that is associated with commercial documents. (The term Internet is used herein as a generic term for a collection of distributed, interconnected networks (ARPANET, DARPANET, World Wide Web, or the like) that are linked together by a set of industry standard protocols (e.g., TCP/IP, HTTP, UDP, and the like) to form a generally global, distributed network. Private and proprietary intranets are also known and are amenable to conforming uses of the present invention.) Further, the user quite often reads such hard copy only once and then discards it or stores it for future reference.
However, currently working against the clear advantages of electronic document distribution, computer displayed documents are of significantly poor quality relative to hard copy print and, at the least, less comfortably read. Standard cathode ray tube (CRT) and matrix liquid crystal displays (LCD) operate at resolutions approximately an order of magnitude lower than commercial print. As a result, the document image is usually magnified on display for better viewability but allowing only a fraction of a standard document page to be viewed at one time. Small character and image detail such as serifs and thin lines are lost, while larger character and image details are aliased or made fuzzy by grey-scaling the original data. Moreover, CRT displays are not portable and require the user to read documents at essentially fixed focal length and fixed body position for long periods of time, leading to eye and body discomfort. Flat panel, matrix LCD devices are lighter weight and more portable for easier focal distance and body repositioning, but are of poorer contrast and limited available viewing angle, leading to further reading discomfort and annoyance. Viewability of such displays also is affected by the ambient lighting in which the apparatus is being used; the higher the ambient light conditions, the worse the viewability of the displayed image or information.
FIG. 1AA (Prior Art) exemplifies the basic operation of a flat panel electronic display, such as a commercially available, flat panel, LCD 1 (dashed lines are used in this drawing to indicate continuation of discrete elements of the apparatus so as to make the drawing less complicated). Basically, the LCD 1 includes a plurality of picture elements (“pixels”) defining the resolution of the display, generally formed by an array of thin film transistors (“TFT”) and too small to be seen in this FIGURE (e.g., 600 dots per inch (“dpi”)). A plurality of gate lines 2 and data lines 3 form a pixel control grid for active area “B” of the panel 1. The gate lines 2 and data lines 3 extend as leads 5 outside of the active area B for connection to known manner integrated circuit drivers. A plurality of pads, one for each line, are formed in region “C” about the periphery of the active area B as discrete pad regions 4 are coupled by the leads 5 to the gate and data lines 2, 3. Color LCD is produced by backlighting the individually switched pixels crystals through color filters. Note importantly that the resolution of the screen is limited by the technology related to interconnect wiring—namely, between the gate and data lines and the microprocessor or memory sending data—and driver size for each pixel. Moreover, such a device requires power to maintain each pixel in its current state and continually to backlight the crystal screen.
Electrostatically polarized, bichromal particles for displays have been known since the early 1960's. There are at least two, well-published, electrochromic pixel coloring devices: (1) a microencapsulated electrophoretic colorant (electronic ink), and (2) a field rotatable bichromal sphere (e.g., the Xerox™ Gyricon™).
Electronic ink is a recent development. E Ink Corporation (Cambridge, Mass.; www.eink.com) provides an electronic ink in a liquid form that can be coated onto a surface. Within the coating are tiny microcapsules (e.g., about 30 μm to 100 μm in diameter, viz. about as thick as a human hair, thus quite visible to the naked eye). As illustrated in FIG. 1BB (Prior Art), each microcapsule 6 has white particles 7 suspended in a dark dye 8. When an electric field is applied and sustained in a first polarity, the white particles move to one end of the microcapsule where they become visible; this makes the surface appear white at that spot. A carrier 9 is provided. An opposite polarity electric field pulls the particles to the other end of the microcapsules where they are substantially hidden by the dye; this makes the surface appear dark at that spot.
The Xerox Gyricon sphere is described in certain patents. FIG. 1CC (Prior Art) is a schematic illustration of the sphere. U.S. Pat. No. 4,126,854 (Sheridon '854) describes a bichromal sphere having colored hemispheres of differing Zeta potential that allow the spheres to rotate in a dielectric fluid under influence of an addressable electrical field. U.S. Pat. No. 4,143,103 (Sheridon '103) describes a display system using bichromal spheres in a transparent polymeric material. U.S. Pat. No. 5,604,027 (Sheridon '027), issued Feb. 18, 1997, for SOME USES OF MICROENCAPSULATION FOR ELECTRIC PAPER, describes a printer. Essentially, each sphere 10 (again, about 30 μm in diameter) has a bichromal ball 13 having two hemispheres 11, 12, typically one black and one white, each having different electrical properties. Each ball is enclosed within a spherical shell 14 and a space 15 between the ball and shell is filled with a liquid to form a microsphere so that the ball is free to rotate in response to an electrical field. The microspheres can be mixed into a substrate which can be formed into sheets or can be applied to a surface. The result is a film which can form an image from an applied and sustained electrical field. Currently picture element (“pixel”) resolution using this Gyricon spheres is limited to about 100 dpi.
Thus, in the known prior art, each individual colorant device is roughly hemispherically bichromal; one hemisphere is made the display background color (e.g. white) while the second hemisphere is made the print or image color (e.g. black or dark blue). In accordance with the text and image data, these microsphere-based devices are field translated or rotated so the desired hemisphere color faces the observer at each respective pixel. It can be noted that, in commercial practice, displays made from these colorants have relatively poor contrast and color. The layer containing the microcapsules is generally at least 3 or 4 microcapsules thick. Light that penetrates beyond the layer surface internally reflects off the backside hemispheres causing color (e.g. black and white) intermixing. This is caused by incomplete absorption or reflection of light by the surface of the microspheres and by light penetrating to sub-layers via the interstitial spaces between microspheres in each layer. The image is, for example, thus rendered dark gray against a light gray background. Thus, these technologies do not provide a promising extendability and scalability to high resolution color displays because the devices switch only between two opaque colors, disallowing passage of light from different layers for a given pixel. Still further, as is these technologies produce a visually poor display resolution relative to hard copy print due to the relatively large size of the microcapsule spheres. Moreover, the spheres are bichromal, limiting application to two color rather than true full color display. Further still, the need for overlapping spheres in multiple layers to achieve adequate color density limits pixel resolution. Yet another limitation is that these technologies suffer from poor pixel switching times in comparison to standard CRT and LCD technology. Each technology relies on the electrophoretic movement of a mass in a dielectric material, such as isoparafin. The color rotation speed of dichroic spheres under practical electrical field intensities is in the range of 20 milliseconds (ms) or more. These relatively large spheres require high switching voltages (e.g. 80–200 volts) to obtain adequate fields through the consequently thick (>100 μm) carrier-colorant layer. Such switching voltages add high cost to the pixel drive electronics, similar to that of the high-end matrix LCD apparatus. Thus, those involved in the development of microcapsule type colorants are struggling with the contrast, resolution, and speed rather than focusing on a new molecular level technology as described in accordance with the present invention.
There is a need for a method and apparatus which will overcome the problems and shortcomings of the state of the art and provide a cost-efficient, erasable and reusable, high contrast, high resolution displays, methods of displaying documents, and methods of doing business related thereto.